Quinodimethane compositions

ABSTRACT

This invention provides a novel class of quinodimethane compounds which can exhibit nonlinear optical response. 
     In one embodiment this invention can provide a high performance nonlinear optical substrate which comprises a transparent organic polymer film containing an array of charge asymmetric molecules such as 13,13-diamino-14,14-dicyanodiphenoquinodimethane: ##STR1##

BACKGROUND OF THE INVENTION

It is known that organic and polymeric materials with large delocalizedπ-electron systems can exhibit nonlinear optical response, which in manycases is a much larger response than by inorganic substrates.

In addition, the properties of organic and polymeric materials can bevaried to optimize other desirable properties, such as mechanical andthermoxidative stability and high laser damage threshold, withpreservation of the electronic interactions responsible for nonlinearoptical effects

Thin films of organic or polymeric materials with large second-ordernonlinearities in combination with silicon-based electronic circuitryhave potential as systems for laser modulation and deflection,information control in optical circuitry, and the like.

Other novel processes occurring through third-order nonlinearity such asdegenerate four-wave mixing, whereby real-time processing of opticalfields occurs, have potential uti-ity in such diverse fields as opticalcommunications and integrated circuit fabrication.

Of particular importance for conjugated organic systems is the fact thatthe origin of the nonlinear effects is the polarization of theπ-electron cloud as opposed to displacement or rearrangement of nuclearcoordinates found in inorganic materials.

Nonlinear optical properties of organic and polymeric materials was thesubject of a symposium sponsored by the ACS division of PolymerChemistry at the 18th meeting of the American Chemical Society,September 1982. Papers presented at the meeting are published in ACSSymposium Series 233, American Chemical Society, Washington, D.C. 1983.

The above-recited publications are incorporated herein by reference.

Of more specific interest with respect to the present inventionembodiments is prior art relating to tetracyanoquinodimethane compounds,such as U.S. Pat. Nos. 3,115,506; 3,226,389; 3,408,367; 3,681,353;3,687,987; 3,953,874; 4,229,364; and 4,478,751.

There is continuing research effort to develop new nonlinear opticalorganic systems for prospective novel phenomena and devices adapted forlaser frequency conversion, information control in optical circuitry,light valves and optical switches. The potential utility of organicmaterials with large second-order and third-order nonlinearities forvery high frequency application contrasts with the bandwidth limitationsof conventional inorganic electrooptic materials.

Accordingly, it is an object of this invention to provide organiccompositions which are characterized by a large delocalized conjugatedπ-electron system which can exhibit nonlinear optical response.

It is another object of this invention to provide a novel class oforganic compounds which is characterized by a charge asymmetricquinodimethane conjugated structure.

It is a further object of this invention to provide high performancenonlinear optical substrates.

Other objects and advantages of the present invention shall becomeapparent from the accompanying description and examples.

DESCRIPTION OF THE INVENTION

One or more objects of the present invention are accomplished by theprovision of a novel class of charge asymmetric conjugatedquinodimethane compositions.

The term "charge asymmetric" as employed herein refers to the dipolaritycharacteristic of organic molecules containing an electron-withdrawinggroup which is in conjugation with an electron-donating group.

Illustrative of the invention class of compositions are quinodimethanecompounds corresponding to the structural formula: ##STR2## where R andR¹ are substituents selected from hydrogen and aliphatic, alicyclic andaromatic groups containing between about 1-20 carbon atoms; n is aninteger with a value between about 1-3; and at least one of the Rsubstituents is an electron-withdrawing group, and at least one of R¹substituents is an electron-donating group.

Each pair of R and R¹ substituents, respectively, can consist of thesame or different groups.

Illustrative of R electron-withdrawing substituents are cyano, nitro,trifluoromethyl, tricyanoethylene, and the like. R alternatively can behydrogen or an aliphatic, cycloaliphatic or aromatic group such asmethyl, chloroethyl, methyoxyethyl, pentyl, decyl, 2-propenyl,2-propynyl, cyclohexyl, phenyl, tolyl, and the like.

The [R₂ C═ moiety can also represent a cyclic structure which iselectron-withdrawing, such as: ##STR3##

Illustrative of R¹ electron-donating substituets are amino, alkylamino,alkenylamino, alkynylamino, alkoxy, thioalkyl, phosphinyl, and the like.R¹ alternatively can be hydrogen or an aliphatic, cycloaliphatic oraromatic group as described for the R substituent above.

The ═CR¹ ] moiety can also represent a cyclic structure which iselectron-donating, such as: ##STR4##

Illustrative of preferred quinodimethane compounds are those in whichthe pair of R substituents are the same electron-withdrawing groups, andthe pair of R¹ substituents are the same electron-donating groups.

An important aspect of the present invention is the provision of aquinodimethane type compound which has utility as a charge asymmetriccomponent of nonlinear optical substrates.

Quinodimethane compounds of particular interest are those which have acharge asymmetric diphenoquinodimethane conjugated structure.Diphenoquinodimethane structures of preference are those correspondingto the formulae: ##STR5## where R is hydrogen or an alkyl group.Illustrative of alky groups are methyl, ethyl, propyl, isopropyl, butyl,isobutyl, pentyl, decyl, hexadecyl, eicosyl, and the like. Alkyl groupscontaining between about 1-20 carbon atoms are preferred. The NR₂ groupcan also represent a heterocyclic structure such as piperidyl, piperizylor morpholinyl.

The ═C(NR₂)₂ moiety in the formulae can constitute a heterocyclicradical in which the two amino groups taken together with the connectingmethylidene carbon atom form a cyclic structure such as imidazoline inthe diphenoquinodimethane compounds: ##STR6##

The diphenoquinodimethane compounds can also contain substituents whichhave one or more optically active asymmetric centers, such as chiralisomeric structures corresponding to the formulae: ##STR7##

In all of the quinodimethane structural formulae illustrated herein thecyclic groups can have one or more of the hydrogen positions on the ringcarbon atoms replaced with a substituent such as alkyl, halo, alkoxy,phenyl, and the like, or can be integrated as part of a more complexfused polycyclic ring structure.

A compound such as 13,13-diamino-14,14-dicyanodiphenoquinodimethane canbe synthesized from 4,4'-dimethyldiphenyl in accordance with thefollowing series of chemical reaction steps; ##STR8##

A compound such as13,13-diamino-14,14-dicyano-4,5,9,10-tetrahydropyrenequinodimethane canbe synthesized from mesitylene by the following series of chemicalreaction steps: ##STR9##

Nonlinear Optical Properties

A quinodimethane compound of the present invention can be utilized as acharge asymmetric component of a nonlinear optical substrate.

Thus, in another embodiment this invention can provide a nonlinearoptical organic substrate exhibiting a X.sup.(2) susceptibility of atleast about 3×10⁻⁶ esu, and wherein the substrate comprises anoncentrosymmetric configuration of molecules having a quinodimethanestructure corresponding to the formula: ##STR10## where R and R¹ aresubstituents selected from hydrogen and aliphatic, alicyclic andaromatic groups containing between about 1-20 carbon atoms; n is aninteger with a value of 1, 2 or 3; and at least one of the Rsubstituents is an electron-withdrawing group, and at least one of R¹substituents is an electron-donating group. R and R¹ are substituents ofthe type previously defined and illustrated.

In another embodiment this invention can provide a nonlinear opticalorganic substrate exhibiting a X.sup.(2) susceptibility of at leastabout 3×10⁻⁶ esu, an absence of interfering fluorescence in thewavelength range between about 0.3-3 μm, an optical loss less than about0.1 decibel per kilometer, a response time less than about 10⁻¹³ second,phase matching of fundamental and second harmonic frequencies, adielectric constant less than about 5, and wherein the substratecomprises a noncentrosymmetric configuration of molecules having aquinodimethane conjugated structure corresponding to the formula:##STR11## where R is a substituent selected from hydrogen and alkylgroups.

In another embodiment this invention can provide a nonlinear opticalorganic substrate exhibiting a X.sup.(2) susceptibility of at leastabout 3×10⁻⁶ esu, an absence of interfering fluorescence in thewavelength range between about 0.3-3 μm, an optical loss less than about0.1 decibel per kilometer, a response time less than about 10⁻¹³ second,phase matching of fundamental and second harmonic frequencies, adielectric constant less than about 5, and wherein the substratecomprises a noncentrosymmetric configuration of molecules having aquinodimethane conjugated structure corresponding to the formula:##STR12## where R is a substituent selected from hydrogen and alkylgroups.

The quinodimethane molecules can have an external field-induced uniaxialmolecular orientation in a host liquid medium, or an externalfield-induced stable uniaxial molecular orientation in a host solidmedium. A substrate of unaligned quinodimethane molecules exhibits thirdorder nonlinear optical response.

In another embodiment this invention can provide an opticallytransparent medium comprising a noncentrosymmetric or centrosymmetricconfiguration of a 13,13-diamino-14,14-dicyanodiphenoquinodimethane typeor a 13,13-diamino-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethanetype of molecules.

In a further embodiment this invention can provide a nonlinear opticalmedium comprising a solid polymeric substrate having incorporatedtherein a distribution of13,13-diamino-14,14-dicyanodiphenoquinodimethane or13,13-diamino-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethanemolecules.

The term "Miller's delta" as employed herein with respect to secondharmonic generation (SHG) is defined by Garito et al in Chapter 1,"Molecular Optics:Nonlinear Optical Properties Of Organic And PolymericCrystals"; ACS Symposium Series 233 (1983).

The quantity "delta"(δ) defined by the equation: ##EQU1## where termssuch as ##EQU2## are the linear susceptibility components, and d_(ijk),the second harmonic coefficient, is defined through ##EQU3## TheMiller's delta (10⁻² m² /c at 1.06 μm) of various nonlinear opticalcrystalline substrates are illustrated by KDP (3.5), LiNbO₃ (7.5), GaAs(1.8) and 2-methyl-4-nitroaniline (160).

Such comparative figures of merit are defined over the frequency rangeextending to zero frequency, or equivalently DC, and the polarizationelectrooptic coefficient as described in the publication by Garito et alrecited above.

The term "fluorescence" as employed herein refers to an optical effectin which a molecule is excited by short wavelength light and emits lightradiation at a longer wavelength. The fluorescence effect is describedwith respect to liquid dye lasers in Optoelectronics, An Introduction,pages 233-236, Prentice Hall International, Englewood Cliffs, N.J.(1983).

The term "optical loss" as employed herein is defined by the equation:

    αL=10 log (I.sub.o /I)

where

α=attenuation coefficient ratio of lost light per unit length

L =sample length

I_(o) =intensity of incident light

I=intensity of transmitted light.

The term "optical scattering loss" is defined and measuredquantitatively by

    T.sub.⊥ /T .sub.∥

where T.sub.⊥ is the transmission of optical radiation through the testsample between polarizers perpendicular to each other, and T.sub.∥ isthe transmission between polarizers parallel to each other.

The term "response time" as employed herein refers to numerous physicalmechanisms for nonlinear optical responses and properties of nonlinearoptical materials. The fastest intrinsic response time to lightradiation is a physical mechanism based on electronic excitationscharacterized by a response time of about 10⁻¹⁴ -10⁻¹⁵ seconds. Responsetime is a term descriptive of the time associated with optical radiationcausing promotion of an electron from the electronic ground state to anelectronic excited state and subsequent de-excitation to the electronicground state upon removal of the optical radiation.

The term "phase matching" as employed herein refers to an effect in anonlinear optical medium in which a harmonic wave is propagated with thesame effective refractive index as the incident fundamental light wave.Efficient second harmonic generation requires a nonlinear optical mediumto possess propagation directions in which optical medium birefringencecancels the natural dispersion, i.e., the optical transmission offundamental and second harmonic frequencies is phase matched in themedium. The phase matching can provide a high conversion percentage ofthe incident light to the second harmonic wave.

For the general case of parametric wave mixing, the phase matchingcondition is expressed by the relationship:

    n.sub.1 ω.sub.1 +n.sub.2 ω.sub.2 =n.sub.3 ω.sub.3

where n₁ and n₂ are the indexes of refraction for the incidentfundamental radiation, n₃ is the index of refraction for the createdradiation, ω₁ and ω₂ are the frequencies of the incident fundamentalradiation and ω₃ is the frequency of the created radiation. Moreparticularly, for second harmonic generation, wherein ω₁ and ω₂ are thesame frequency ω, and ω₃ is the created second harmonic frequency 2ω,the phase matching condition is expressed by the relationship:

    n.sub.ω n.sub.2ω

where n.sub.ω and n₂ω are indexes of refraction for the incidentfundamental and created second harmonic light waves, respectively. Moredetailed theoretical aspects are described in "Quantum Electronics" byA. Yariv, chapters 16-17 (Wiley and Sons, New York, 1975).

The term "dielectric constant" as employed herein is defined in terms ofcapacitance by the equation:

ε=C/C_(o)

where

C=capacitance when filled with a material of dielectric constant

C_(o) =capacitance of the same electrical condenser filled with air

The term "external field" as employed herein refers to an electric ormagnetic field which is applied to a substrate of mobile organicmolecules, to induce dipolar alignment of the molecules parallel to thefield.

The term "optically transparent" as employed herein refers to an opticalmedium which is transparent or light transmitting with respect toincident fundamental light frequencies and created light frequencies. Ina nonlinear optical device, a present invention nonlinear optical mediumis transparent to both the incident and exit light frequencies.

The fundamental concepts of nonlinear optics and their relationship tochemical structures can be expressed in terms of dipolar approximationwith respect to the polarization induced in an atom or molecule by anexternal field, as summarized in the ACS Symposium Series 233 (1983).

Field-induced Microscopic Nonlinearity

The microscopic response, or electronic susceptibility β, and itsfrequency dependence or dispersion, is experimentally determined byelectric field induced second harmonic generation (DCSHG) measurementsof liquid solutions or gases as described in "Dispersion Of TheNonlinear Second Order Optical Susceptibility Of Organic Systems",Physical Review B, 28 (No. 12), 6766 (1983) by Garito et al, and theMolecular Crystals and Liquid Crystals publication cited above.

In the measurements, the created frequency ω₃ is the second harmonicfrequency designated by 2ω, and the fundamental frequencies ω₁ and ω₂are the same frequency designated by ω. An applied DC field removes thenatural center of inversion symmetry of the solution, and the secondharmonic signal is measured using the wedge Maker fringe method. Themeasured polarization at the second harmonic frequency 2ω yields theeffective second harmonic susceptibility of the liquid solution and thusthe microscopic susceptibility β for the molecule.

The present invention class of novel organic compounds exhibitsextremely large values of β because of a noncentrosymmetricquinodimethane structure . Illustrative of this class of compounds is13,13-diamino-14,14-dicyanodiphenoquinodimethane (DCNDQA): ##STR13##

The DCNDQA molecule is characterized by a single excited state at 2.2eV(0.6 ); a dipole moment difference of Δρ^(x) ₁ :23D; a transitionmoment of μ^(x) _(1g) :13.6D; and large 2ω and ω contributions to β oforder 10³ at 1μ-0.6μ, and no interfering 2ω resonance from higherexcitations.

FIG. 1 represents a graph of β_(x) relative to hω(eV) for the DCNDQAmolecule. A DCNDQA type of diphenoquinodimethane conjugated structureexhibits nonlinear optical responses which are 2-3 orders of magnitudegreater than those of a chemical structure such as2-methyl-4-nitroaniline.

The theory and practice of high performance nonlinear opticalsubstrates, with specific reference to quinodimethane compounds, iselaborated in copending patent application Ser. No. 748,617, filed June25, 1985; incorporated herein by reference.

The following examples are further illustrative of the presentinvention. The components and specific ingredients are presented asbeing typical, and various modifications can be derived in view of theforegoing disclosure within the scope of the invention.

Fluorescence activity in a nonlinear optical substrate is measured byPerkin-Elmer Fluorescence Spectroscopy Model No. MPF-66 or LS-5.

Optical loss exhibited by a nonlinear optical substrate is measured byoptical time domain reflectometry or optical frequency-domainreflectometry as described in "Single-mode Fiber Optics" by Luc B.Jeunhomme, Marcel Dekker Inc., N.Y., 1984. It is also measured by themethod described in "The Optical Industry And Systems PurchasingDirectory", Photonics, 1984. The scattering optical loss isquantitatively measured by the ratio of perpendicular transmission toparallel transmission of a He-Ne laser beam through the nonlinear samplewhich is placed between crossed polarizers.

The response time of a nonlinear optical substrate is calculated by themethod described in "Optoelectronics; An Introduction" by P. J. Deau,Editor, Prentice-Hall International.

The dielectric constant of a nonlinear optical substrate is measured bythe methods described in Chapter XXXVIII of "Technique of OrganicChemistry", Volume I, Part III, (Physical Methods of Organic Chemistry)by Arnold Weissberger, Editor, Interscience Publishers Ltd., New York,1960.

EXAMPLE I

This Example illustrates the preparation of13,13-diamino-14,14-dicyano-4,5,9,10-tetrapyrenoquinodimethane inaccordance with the present invention.

Ten grams of13,13,14,14-tetracyano-4,5,9,10-tetrahydropyrenoquinodimethane preparedby the synthetic scheme previously described and 2 liters oftetrahydrofuran are placed in a three-necked three-liter flask equippedwith a mechanical stirrer, a nitrogen inlet, a drying tube and agas-inlet connected to an anhydrous ammonia gas tank. Ammonia gas isbubbled through the stirred solution for three days at room temperature.The crude product in precipitate form is filtered from the reactionmixture, washed with distilled water, and recrystallized from DMF-waterto yield high purity13,13-diamino-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethaneproduct. DC induced second harmonic generation can achieve a secondorder nonlinear optical susceptibility β of about 900×10⁻³⁰ esu, anoptical susceptibility X.sup.(2) of about 3.1×10⁻⁶ esu, and a Miller'sdelta of about 4 square meters/coulomb.

When the NLO substrate is centrosymmetric in macroscopic configuration,it can exhibit a nonlinear optical susceptibility X.sup.(3) of about2×10⁻⁹ esu, a response time of less than 10⁻¹³ second, an absence offluorescence in the wavelength range between about 0.3-3 μm, an opticalloss less than about 0.1 decibel per kilometer, and a dielectricconstant less than about 5.

EXAMPLE II

This Example illustrates the preparation of13,13-di(n-hexadecylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethanein accordance with the present invention.

A three-necked three-liter flask equipped with a mechanical stirrer, anitrogen inlet, a drying tube, and an addition funnel is charged with 10grams (0.03 moles) of13,13,14,14-tetracyano-4,5,9,10-tetrahydropyrenoquinodimethane and twoliters of tetrahydrofuran. Twenty-nine grams (0.12 moles) ofn-hexadecylamine in 100 ml of tetrahydrofuran is added dropwise into theflask, and the resulting mixture is stirred for three days at roomtemperature. The resulting THF solution is concentrated on a rotaryevaporator.

The crude product in precipitate form is separated by filtration, washedwith distilled water, neutralized with 10% solution of ammoniumhydroxide, washed with water, and then recrystallized fromN,N-dimethylformamide-water to yield13,13-di(n-hexadecylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane.This compound is aligned in a melt-phase in a DC field by applying about15 Kvolts/cm, and cooled slowly to freeze the aligned molecularstructure in the DC field. The aligned molecular substrate is opticallytransparent and can exhibit a nonlinear optical susceptibility β ofabout 1000×10⁻³⁰ esu, a X.sup.(2) of about 3.3×10⁻⁶ esu, and a Miller'sdelta of about 4 square meters/coulomb.

In a substrate in which the molecules are randomly distributed, theproduct can exhibit a nonlinear optical susceptibility X.sup.(3) ofabout 2×10⁻⁹ esu. The other properties are similar to those describedfor the Example I product.

EXAMPLE III

This Example illustrates the preparation of13,13-diamino-14,14-dicyanodiphenoquinodimethane in accordance with thepresent invention.

Following the procedure of Example I,13,13-diamino-14,14-dicyanodiphenoquinodimethane is prepared by ammoniatreating a tetrahydrofuran solution containing 10 grams of13,13,14,14-tetracyanodiphenoquinodimethane that is obtained by thesynthesis scheme previously described.

DC induced second harmonic generation can provide a nonlinear secondorder optical susceptibility β of about 900×10⁻³⁰ esu in the product.

In a product substrate with a centrosymmetric molecular configuration,the susceptibility X.sup.(3) is about 2×10⁻⁹ esu. The other substrateproperties are similar to those described for the Example I product.

EXAMPLE IV

This Example illustrates the preparation of13,13-di(n-hexyldecylamino)-14,14-dicyanodiphenoquinodimethane.

Following the procedure of Example II,13,13-di(n-hexadecylamino)-14,14-dicyanodiphenoquinodimethane isprepared by employing a tetrahydrofuran solution containing ten grams of13,13,14,14-tetracyanodiphenoquinodimethane and thirty-two grams ofn-hexadecylamine. The second order nonlinear susceptibility μis about800×10⁻³⁰ esu after alignment of molecules in a DC field, or afteralignment of molecules by the Langmuir-Blodgett Technique in which amonolayer or several layers of molecules are deposited on a glasssubstrate.

EXAMPLE V

This Example illustrates the use of13,13-di(n-hexyldecylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethaneas a guest molecule in a polymer substrate.

Ten grams of13,13-di(n-hexadecylamino)-14,14-dicyano4,5,9,10-tetrahydropyrenoquinodimethaneand 90 grams of poly(methyl methacrylate) are dissolved in 400 ml ofmethylene chloride. A film (2 mil) is cast from this solution on a glassplate coated with indium tin oxide. Another glass plate coated withindium tin oxide is placed on the film, and then the film is heated toabout 150° C. A DC field is applied to align the molecules, and the filmis cooled slowly in the applied field to yield an aligned polymer alloywhich can have a second order nonlinear susceptibility β of about1000×10⁻³⁰ esu.

What is claimed is:
 1. A diphenoquinodimethane composition correspondingto the structure: ##STR14## where R is a substituent selected fromhydrogen and alkyl group containing between about 1-20 carbon atoms. 2.A diphenoquinodimethane composition corresponding to the structure:##STR15## where R is a substituent selected from hydrogen and alkyigroups containing between about 1-20 carbon atoms. 3.13,13-Diamino-14,14-dicyanodiphenoquinodimethane. 4.13,13-Di(dimethylamino)-14,14-dicyanodiphenoquinodimethane. 5.13,13-Di(diethylamino)-14,14-dicyanodiphenoquinodimethane. 6.13,13-Di(n-hexydecylamino)-14,14-dicyanodiphenoquinodimethane. 7.13,13-Diamino-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane. 8.13,13-Di(dimethylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane.9.13,13-Di(diethylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane.10.13,13-Di(n-hexadecylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane.